The invention relates to vehicle traffic sensing systems, and more particularly to vehicle traffic sensing systems using residual charge-effect sensing.
It has become apparent several improvements could be made by eliminating the conductive mounting bar disclosed in U.S. Pat. No. 5,835,027. The manufacturing cost could be significantly reduced, the data reliability could be increased to 100% and the field use could be more-user friendly. During the manufacturing process, the conductive mounting bar was hard to handle due to its weight. The automated equipment designed to fabricate these sensors was expensive and very large in size. Also, a complex design of rollers was required to open and close the conductive elastomeric material which totally encapsulated the conductive mounting bar and its associated components in order to make this assembly watertight. These procedures were workable, but they would have a negative impact on the sensor marketability. The sensor vehicle data output voltage signals were 100% accurate most of the time, but intermittently dropped to less than 100%. Four causes were identified for this condition:
(1) It was determined the adhesive bonding the signal wires to the conductive mounting bar were becoming detached and in effect these wires were turning into sensors due to their close proximity to the conductive elastomeric material.
(2) It was determined on hot dry days the rotating tires on the vehicles were generating and accumulating a static charge and sometimes this static charge would be released to the roadway sensor causing an unwanted signal to appear or negate a valid signal.
(3) Heavy trucks, e.g. large dump trucks carrying sand and loaded cement trucks, would generate unwanted signals due to the conductive elastomeric material collapsing onto the transmitting signal wires turning them into sensors.
(4) Due to capacitance coupling between the wires within the multi-conductor cable between the sensor and the data record, erroneous signals were being introduced to the data records input circuitry.
It was determined after repeated usage of the sensor at multiple different locations that the conductive mounting bar was distorting between the hold-down clamps within the traffic lanes. This distortion was in the form of a six to eight inch arc in the direction of the traffic flow. Although this distortion did not cause a noticeable operational loss in signal, it had an effect on the timing of signals from two sensors when the data record is calculating the speed of the vehicle. The physical change made it very time-consuming to recover the sensor from the roadway when it came time to secure the sensor onto a reel which has a fixed dimension of two inches. This arc was caused by the conductive mounting bar taking a set in the material and made it difficult to wind it on the reel for transport to the next installation. The only practical method of placing the sensor on the reel was to lay the sensor parallel to the roadway and straighten out the arc with the use of a hammer and a long piece of wood. This procedure would not meet the minimum safety standards set by Department of Transportation""s in the USA.
The present invention was developed to overcome the aforementioned problems experienced during the manufacturing process and subsequent field testing. The roadway traffic sensor was simplified by removing the conductive mounting bar and several other novel methodology were employed to significantly improve the performance and reduce the manufacturing costs of this roadway traffic sensor.
Accordingly, a primary object of the present invention is to provide an improved portable traffic sensor which is relatively inexpensive to produce, is durable, very accurate, easily and safe to deploy. It will be used to monitor singular or multiple independent lanes of traffic simultaneously. A secondary object of this invention is to slightly vary the three basic components of the portable roadway sensor resulting in a permanent roadway sensor which can be installed within the surface of concrete or asphalt roadways.
It is a more specific object of the invention to provide a traffic sensor including an elastomeric extrusion containing one or more longitudinal grooves with one of its sides open to be subsequently closed using an adhesive backed tape. At least one sensing element or a parallel group of sensing elements per lane supported within the extrusion which generates signals when impacted by the tire of a vehicle. A signal transmission wire securely bonded within the groove of the elastomeric extrusion connected to the sensing element for transmitting these signals to a cable arrangement connected to analyzing equipment for evaluation, displaying and storing vehicle data generated by the sensing element.
The sensor is characterized by a first electrode or conductor, a first dielectric in intimate contact with the first electrode which carries a residual charge that migrates to the first electrode/first dielectric interface when placed in intimate contact therewith, a second dielectric arranged adjacent to the first dielectric, and a second electrode or conductor arranged adjacent to the second dielectric . The first electrode and dielectric may be, for example, an ordinary insulated electrical wire such as a wire coated with a synthetic resin polymer (Teflon) and the second dielectric may be an air gap which surrounds some of the wire. Certain other materials such as paper exhibiting a residual charge may also be used as one of the dielectrics.
It is another object of this invention to minimize cross-talk between the transmitting signal wires within the elastomeric extrusion by taking advantage of the conductive properties of the elastomeric extrusion by nesting them in grooves.
It is another object of this invention to significantly improve the signal to noise ratio by securely bonding the transmitting signal wires to the base of the grooves within the elastomeric extrusion.
It is another object of this invention to eliminate the cross-talk between the wires of the transmission signal wire cable between the roadway sensor and the analyzing equipment with the use of a special purpose electronic amplifier circuit.
It is another object of this invention to eliminate vehicle generated static voltage discharge from appearing or negating valid sensor signals on the transmitting signal wires connected to the analyzing equipment with an earth ground connection to the elastomeric extrusion.
It is another object of this invention to significantly increase the signals energy by using parallel groups of ordinary insulated wire coated with a synthetic resin polymer.
It is another object of this invention to differentiate between lightweight and heavyweight vehicles and store a unique code representing this difference.
It is another object of this invention to reduced the manufacturing cost, weight and ease of deployment of the roadway traffic sensor by eliminating the conductive mounting bar.
It is another object of this invention to provide a traffic sensor having an access opening in the elastomeric extrusion thereby affording easy access to the component parts of the roadway traffic sensor.
It is another object of this invention to provide a traffic sensor that has a low profile and can be either mounted on the surface of the roadway or embedded within the roadway.
It is another object of this invention to provide a traffic sensor which operates in a non-directional mode.
It is a further object of the present invention to provide a traffic sensor which can be used with existing traffic analyzing equipment.